As part of testing do a trial scrutinering of your car to ensure it meets the regulations.
Check all the items listed in the CURRENT regulations, as the regulations change every
year.
17 Aerodynamics
Air drag has a much larger effect on car performance than most people realise.
Wind tunnel testing of 2 models, one a simple box the other an aerofoil shape gave us
aerodynamic drag figures for these shapes. When these drag figures were used in the
Mathematical Simulation to obtain predicted race results indications were that simply
changing the car shape from the box to the aerofoil shape all other parameters remaining
the same would result in a win for the aerofoil shape by about 8 meters over a 1 lap race
and about 23 meters for a 2 lap race.
See Appendix L for complete test results.
Aerodynamics is a complex subject so all we will do is give a simple overview to point
you in the right direction. Refer to texts and other publications for a more detailed
analysis.
The aerodynamic drag force is trying to slow your car, the drag force can be calculated
using the formula below.
Drag Force = ½ x Air Density x Drag coefficient x Area x Velocity squared
There are only two parameters in this formula that you can work on. They are:
- Drag coefficient, which is related to the shape of your car. Typically
smooth rounded curves with an aerofoil type shape will give a low drag
coefficient. Refer to texts for details but remember it takes a lot of effort
and attention to detail to produce a car with a low drag coefficient. - Area, which is frontal area. The area that is pushed through the air as the
car runs forward. (We will ignore the effect of wind which could be
coming from any direction) Frontal area is relatively easy to control. Just
make your car as small as possible within the regulations. If you can halve
the frontal area you will halve the drag force.
For a single lap race aerodynamic drag is a significant retarding force by the end of the
race when the car velocity is high. For a two lap race the whole of the second lap is run at
high speed making the aerodynamic drag even more important.
See Appendix K for photographs of some cars and their drag coefficients for use in
the Mathematical simulation. And Appendix L for Car Shape and Aerodynamic
Drag.
I am often confronted with the suggestion that useful lift to reduce wheel load and hence
rolling resistance or down force to hold the car onto the track can be generated
aerodynamically. It is true these forces exist and are used to great effect on formula 1 and
other race cars, but I question the usefulness of them in Model Solar Car racing. For a
normal car considering car area together with the maximum expected velocity these